European Patent Application No. 09013565.8 discloses a system which is provided for use in a wind turbine which comprises a rotor having two or more blades in order to measure a wind speed field, at least one sensor signal being obtained by measuring at least at one of the rotor blades a physical property which is characteristic of at least one characteristic variable of the wind speed field. There is produced for a plurality of wind conditions a table which places the at least one sensor signal in relation to values for the at least one characteristic variable of the wind speed field. A value for the at least one characteristic variable of the wind speed field is established from the table by means of a search unit on the basis of values which are given for a current wind condition and which characterise the at least one sensor signal.
The electrical power produced by a wind turbine is of great interest and financial significance both for the wind turbine manufacturer and for the wind turbine operator. The power produced momentarily by a wind turbine depends, on the one hand, on the state of the mechanical equipment components, including the rotor blades, the drive train, the electrical components and the control of those equipment components and, on the other hand, characteristic variables of the wind, such as the wind strength, the wind direction relative to the rotor orientation and the horizontal and vertical wind shear, in the region of the surface-area covered by the rotor. These characteristic variables are specific to the location of the wind turbine and depend both on the geographical location thereof and on atmospheric conditions. Furthermore, if a plurality of wind turbines are positioned close together in a wind park, a wind turbine may further influence the electrical power production of another wind turbine owing to the wind shadow thereof.
The expected electrical power which generally forms part of the contractual obligations between the manufacturer and operator is generally defined by general conditions which are set out by the manufacturer, such as, for example, the operation of the wind turbine on level ground with constant wind. Disputes may arise between the parties if the power actually produced does not correspond to the expected power. Consequently, there is a need both for the manufacturer and for the operator for a method which allows precise and reliable estimation of the operating state of the wind turbine in order to be able to check whether the actual power of the wind turbine corresponds to the specifications of the manufacturer.
A precise estimation of the electrical power currently produced by the wind turbine over the service-life thereof would further afford the advantage to the operator of identifying problems in mechanical equipment components of the wind turbine by comparison of the estimated value for the electrical power with the measured value for the electrical power if the estimated value and the measured value deviate from each other by more than a predetermined amount (the estimated value for the electrical power may also be referred to as expected electrical power).
Currently, it is not possible to establish an estimated value for the electrical power at a specific location either momentarily or over a period of time with a sufficient level of accuracy because the characteristic variables of the wind in the surface-area covered by the rotor are not known. The measurement devices arranged at the upper end of the gondola, such as an anemometer and wind vane, are too imprecise because they only measure the wind at a single spatial point and not in the surface-area covered by the rotor. Distortions in the wind field further occur owing to the gondola and turbulence generated by each blade, whereby precise measurement is prevented.
Wind data of greater quality can be provided by a meteorological mast. The spacing between the mast and the wind turbine results in unknown deviations of the wind speed at the location of the rotor, however, whereby the calculation of an accurate estimated value for the electrical power is prevented. This aspect becomes even more problematic if only a single mast or a small number of masts is/are used for a large wind park which may comprise up to several hundred wind turbines which are arranged so as to be distributed over a large area. Although a reduction in the spacing between the masts and the wind turbines by using a large number of masts would reduce the problem, the expenditure necessary for this would be too great and too cost-intensive. Another disadvantage is that each mast can measure the wind shear only in the vertical direction so that the horizontal wind shear remains unknown.
Although optical systems mounted on the gondola such as, for example, LIDAR systems (LIDAR=light detection and ranging) can measure through the rotor plane into the incoming wind field, the measurement takes place only along a laser beam so that the detectable range from the measurement position is limited to a cone whose interface with the surface-area covered by the rotor is only a portion thereof. Consequently, the characteristic variables of the wind can be measured only in an inadequate manner over the surface-area covered by the rotor.
Therefore, it is desirable to provide a system and/or method which is preferably available at any time for establishing a precise estimated value for the electrical power of a wind turbine.